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TPS40210: About RC capacitor value

Satoshi
Guru 19685 points

Part Number: TPS40210

Please let me know about two points below for RC capacitor value;

①Datasheet page-15 is described "capacitor in the range of 68 pF to 120 pF gives the best results", but page-6 Figure-1 graph is 33pF~470pF.

　Which is correct recommended range?

②If Rt is 470pF or more large, what is the possible to problem?

【Background】

Some TPS40210 is no switching (and no output) because RC voltage was not rise.

I looking for possibility of the reason.

Best regards,

Satoshi

  • 0
    TI__Mastermind 21720 points
    Hi Satoshi,

    Below are my comments to your questions.

    ①Datasheet page-15 is described "capacitor in the range of 68 pF to 120 pF gives the best results", but page-6 Figure-1 graph is 33pF~470pF.

    The best range is going to be in the 68pF to 120pF range. This is due to the resistor selection for more common switching frequencies being more common resistor values. That being said any range from 33pF to 470pF should yield normal performance.

    Can you please send over the schematic? Also, is there normal operation when the VDD rail is at steady state?

    Thanks

    Garrett
  • 0 in reply to Garrett Roecker
    Guru 19685 points

    Garrett-san

    Thank you for reply,

    Sorry, schematic can't attach on E2E because customer confidential.

    The other information is below;

    ・VDD rail is 13V and steady state.

    ・R_RC：300kΩ, C_RC：470pF(50V)

    　⇒fsw is about 160kHz

    ・One board was occurred this problem, the other board was normal operation (please see attached below). 

    I think that this causing is C_RT or TPS40210 internal circuit.

    If there any cause or confirming point, please let me know.

    Best regards,

    Satoshi

  • 0 in reply to Satoshi
    TI__Mastermind 21720 points
    Hi Satoshi,

    Please make sure that the values on the RC pin are correct. You can send the schematic directly to me (g-roecker@ti.com) for review.

    Thanks,

    Garrett